Here is another independent Exile amplifier test. It's the Harpoon which is rated at 500 watts per channel into a 2-ohm load according to CEA RMS standards (1% distortion, 14.4 V supply).
As tested,...

Ideally you would want identical power to all four 10-inch drivers in a Wetsounds 3-Some. The single center Rev410 has the same 4-ohm impedance load as the two outside Rev10s, so managing this is not...

On second thought, if you wanted something more than a 10-inch HLCD, look no farther than the Rev410. The dual sealed dustcap 10"s give you better than 45% more surface area versus a single proaxial...

All good advice above from Frank, Brett, Mike and the others. You've already establish that the voltage increases by a fair margin when the engine is running. I would not trust my alternator voltage...